1. Field of the Invention
The present application relates generally to the field of guard columns for high-pressure liquid chromatography (HPLC) devices. Guard columns are generally used to protect HPLC columns from physical or chemical contamination.
2. Description of the Related Art
High-pressure liquid chromatography (HPLC) is a process used for separating one or more compounds from a chemical mixture. The HPLC process consists of passing the mixture through a stationary packing material, under the influence of a high-pressure transport liquid, and separating the compounds by selective affinity, sieving, absorption or partition. The packing is typically housed within a thru-bored section of a body of a column and is typically held in place by frits at either end of the body.
FIG. 1 illustrates a typical HPLC apparatus 10 according to the related art wherein a chemical mixture is injected into the HPLC apparatus 10 through an injection apparatus 300. The mixture first passes through the frits 120, 140 and packing 115 of a guard column 30. Then, the mixture is xe2x80x9cfunneledxe2x80x9d through a narrow opening of a capillary connector 40 that is located between the guard column 30 and an HPLC column 20. From that point, the mixture flows through the frits 180, 200 and packing 170 of the HPLC column 20 and the components of the mixture can then travel through an exit apparatus 340 after which they can be measured, collected, redirected or disposed of.
The typical HPLC apparatus 10 illustrated in FIG. 1 shows the guard column 30 contained within a housing 45 and held in place by a threaded top end fitting 310. The top end fitting 310 is screwed onto an end of the housing 45. Because of the extreme pressures sometimes used to conduct HPLC processes (e.g., pressures up to and above 6,000 pounds per square inch (psi)), the top end fitting 310 is typically screwed to the housing 45 using wrenches or other methods of supplying high torque.
The injection apparatus 300 through which the mixture enters the HPLC apparatus 10 is sheathed within the top end fitting 310. A small region of the top end fitting 310 can form a top end fitting pathway 12 through which the mixture travels before flowing into the guard column 30.
The guard column 30 is positioned between the top end fitting 310 and the housing 45. To prevent leaks, a guard column top seal 90 is placed between the guard column 30 and the top end fitting 310 and a guard column bottom seal 70 is placed between the guard column 30 and the housing 45.
The guard column 30 is removable and replaceable. To remove the guard column 30, the top end fitting 310 is unscrewed from the housing 45 and the guard column 30 is pulled out. The guard column 30 can then be inspected and, if necessary, replaced. An advantage of a replaceable guard column 30 is that the HPLC column 20, which is substantially more expensive than the guard column 30, does not have to be replaced as often, if ever. The guard column 30 traps impurities or particulates in the sample mixture or in the transport liquid before the impurities or particulates can reach the HPLC column 20 and thereby extends the operable lifetime of the HPLC column 20.
The capillary connector 40 can be a piece of tubing or other device that connects the guard column 30 to the HPLC column 20. It is, according to FIG. 1, held in place by a top capillary fitting 22 and a bottom capillary fitting 23.
The capillary connector 40 abruptly changes the cross-sectional area of the path of the mixture by forcing the mixture to flow from the thru-bore section of the guard column 30 to the relatively narrow opening of the capillary connector 40. Then, the mixture passes through a relatively large thru-bore section of the HPLC column 20. The sudden changes in the cross-sectional area of the flow path disrupt the flow of the mixture, cause unwanted mixing and blending of the mixture, and lower the capability of the HPLC column 20 to separate compounds from the mixture (i.e., causes band-spreading).
An improvement to the HPLC apparatus 10 design depicted in FIG. 1 exists in the related art. This improvement eliminates the capillary connector 40 by making the guard column 30 xe2x80x9cintegralxe2x80x9d to the HPLC column 20.
FIG. 2 illustrates such an alternative HPLC apparatus 10, according to the related art, wherein a chemical mixture is injected into the HPLC apparatus 10 through an injection apparatus 300. The mixture first passes through the frits 120, 140 and packing 115 of a guard column 30 that sits in a guard column housing 45. Then, the mixture is xe2x80x9cfunneledxe2x80x9d through a narrow opening that is located on the exit end of the guard column housing 45. From that point, the mixture flows through the frits 180, 200 and packing 170 of the HPLC column 20 and the components of the mixture can then travel through an exit apparatus 340, after which they can be measured, collected, redirected or disposed of.
The components of the HPLC apparatus 10 illustrated in FIG. 2 are contained within an assembly comprised of an externally threaded bottom end fitting 360 and an internally threaded top end fitting 310. This assembly is held in place by engaging two upper grommets 350 that fit into an upper groove 380 that is machined into the outer wall of the HPLC column 20. Because of the extreme pressures sometimes used to conduct HPLC processes (e.g., pressures up to and above 6,000 psi), the top end fitting 310 and the bottom end fitting 360 are typically screwed together using wrenches or other methods of supplying high torque.
The injection apparatus 300 through which the mixture enters the HPLC apparatus 10 is sheathed within the top end fitting 310. A small region of the top end fitting 310 can form a pathway 12 through which the mixture travels before flowing into the guard column 30.
The guard column 30 is enclosed in a guard column housing 45 and positioned between the top end fitting 310 and the HPLC column 20. To prevent leaks, a guard column top seal 90 is placed in the guard column housing 45 above the top end of the guard column 30. This guard column top seal 90 mates with the exit end of the top end fitting 310 to form a leak-tight seal. An HPLC column top seal 100 is placed inside the HPLC column 20 to mate with the exit end of the guard column housing 45 to form a leak-tight seal.
The guard column 30 and the guard column housing 45 are removable and replaceable. To remove the guard column 30 and the guard column housing 45, the internally threaded top end fitting 310 is unscrewed from the externally threaded bottom end fitting 360 and the guard column 30 and the guard column housing 45 are pulled out. The guard column 30 can then be inspected and, if necessary, the guard column 30 and the guard column housing 45 can be replaced.
The guard column housing 45 abruptly changes the cross-sectional area of the path of the mixture by forcing the mixture to flow from the thru-bore section of the guard column 30 to the relatively narrow exit opening 42 of the guard column housing 45. Then, the mixture passes through a relatively large thru-bore section of the HPLC column 20. The sudden changes in the cross-sectional area of the flow path disrupt the flow of the mixture, cause unwanted mixing and blending of the mixture, and lower the capability of the HPLC column 20 to separate compounds from the mixture (i.e., causes band-spreading).
Below the guard column housing 45 is the HPLC column top seal 100 that is placed inside the top of the HPLC column 20. An HPLC column bottom seal 110 is placed between the HPLC column 20 and an exit fitting 375 that sheathes the exit apparatus 340. The exit fitting 375, when screwed onto a lower HPLC column fitting 365, holds the exit fitting 375 and the HPLC column 20 together with the use of two lower grommets 385 that fit into a lower groove 395. The end of the exit fitting 375 contains a pathway through which the components of the mixture travel before flowing into the exit apparatus 340, after which they can be measured, collected, redirected or disposed of.
The HPLC column bottom seal 110, the HPLC column top seal 100, and the guard column top seal 90 are typically formed from polymeric materials that are specifically designed and manufactured to withstand the high-pressure and potentially corrosive conditions necessary for HPLC processes. Hence, the seal materials are extremely expensive and each seal increases the overall cost of the HPLC apparatus illustrated in FIG. 2. In addition, the HPLC apparatus in FIG. 1 and in FIG. 2 both require the sample mixture to xe2x80x9cfunnelxe2x80x9d through narrow channels between the guard columns and the HPLC columns. The sudden changes in the cross-sectional area of the flow path disrupt the flow of the mixture, cause unwanted mixing and blending of the mixture, and lower the capability of the HPLC column 20 to separate compounds from the mixture (i.e., causes band-spreading). Accordingly, a need exists for an improved HPLC apparatus 10.
According to one embodiment, a high-pressure liquid chromatography (HPLC) apparatus that includes a top end fitting, a removable, metallic guard column in direct contact with the top end fitting, wherein the guard column includes a guard column inlet and a guard column outlet, and an HPLC column, wherein the HPLC column includes an HPLC column inlet and an HPLC column outlet, and wherein substantially all of the guard column outlet engages the HPLC column inlet.
According to another embodiment, an An HPLC apparatus that includes a hand-tightened top end fitting at a first end of the HPLC apparatus and a hand-tightened bottom end fitting at a second end of the HPLC apparatus wherein the top end fitting and the bottom end fitting provide seals sufficient for operation of the HPLC apparatus, and an HPLC column positioned between the top end fitting and the bottom end fitting, the HPLC column having an HPLC column inlet and an HPLC column outlet, a removable guard column having a guard column inlet and a guard column outlet wherein substantially all of the guard column outlet engages the HPLC column inlet.
According to yet another embodiment, a method of gathering HPLC data that includes hand-tightening a top fitting and a bottom fitting around a removable guard column and an HPLC column engaged with the guard column to provide a seal, injecting an experimental sample into the guard column, and allowing the experimental sample to travel through a path of substantially constant cross-sectional geometry as the experimental sample travels through a guard column outlet, to an HPLC column inlet, and through the HPLC column inlet.